1. Field of the Invention
The invention relates to a supported catalyst which contains ruthenium, palladium or a mixture of both metals and has a support of niobic acid, tantalic acid or a mixture of both. The invention furthermore relates to a process for the preparation of such a catalyst and to a process for the preparation of a mixture of optionally substituted cyclohexylamine and optionally substituted dicyclohexylamine by catalytic hydrogenation of optionally substituted aniline using the catalyst according to the invention.
2. Description of the Related Art
It is known to prepare cyclohexylamine and other ring-hydrogenated amino compounds by catalytic hydrogenation of aniline and other aromatic amino compounds. Catalysts which are known for this purpose are: cobalt catalysts which contain a basic additive (GB 969,542), Raney-Kobalt (JP 68/03180), ruthenium catalysts (German Auslegeschrift 1,106,319), ruthenium catalysts doped with alkali metal compounds (U.S. Pat. No. 3,636,108) or nickel catalysts (German Patent Specification 805,518).
Most of the processes mentioned are carried out under pressure and give mainly cyclohexylamine apart from only a little dicyclohexylamine. Dicyclohexylamine is therefore frequently prepared by other processes, for example by pressure hydrogenation of diphenylamine using a ruthenium catalyst (German Auslegeschrift 1,106,319). Dicyclohexylamine is additionally formed in the reaction of cyclohexanone with cyclohexylamine in the presence of a palladium/carbon catalyst under a hydrogen pressure of about 4 bar (FR 1,333,692). The process of German Patent Specification 805,518 mentioned is mainly directed to the production of dicyclohexylamine, but is carried out with troublesome returns of by-product.
Other disadvantages of the processes mentioned consist in some cases considerable amounts of cyclohexane waste products, as well as in the unsatisfactory working life of the catalysts employed. There was therefore the desire to develop a process which can be used on an industrial scale, in which the loss due to the formation of cyclohexane is decreased and the working life of the catalyst used is improved, and also to develop a process in which cyclohexylamine and dicyclohexylamine are jointly formed in amounts which are variable according to the demand for the two substances mentioned.
Surprisingly, it has been found that the demands mentioned can be met by the use of the supported noble metal catalyst described in the following.